Huntington-Associated-Protein 1 (HAP1) was identified through its interaction with huntingtin, the protein mutated in Huntington's Disease (HD). In HD, huntingtin contains an expanded polyglutamine stretch which affects its interaction with other proteins including an increase in its binding to HAP1. In rodents and primates, HAP1 is mostly found in the brain where it is expressed in neurons. Although several functions have been proposed for HAP1, its physiological role has not been established. To further understand the role of HAP1 we have started studying its C. elegans homologue called T27A3.1. To map out the expression of T27A3.1a-e isoforms we have generated several transgenic worm lines. We have found expression of a fluorescent reporter protein under the control of the promoter for T27A3.1 in a subset of neurons including chemosensory neurons in the head and tail. We have also found T27A3.1 isoforms to be expressed in a similar subcellular localization as of mammalian HAP1. To further understand the role of T27A3.1 we propose 1) to generate antibodies against T27A3.1 and use these antibodies for immunocytochemical localization of the various isoforms both at the cellular and subcellular level, 2) to identify behavioral phenotypes resulting from silencing small sets of T27A3.1 isoforms or from mutational knockout and evaluate the ability of mammalian HAP1 to rescue those phenotypes and 3) to characterize the interaction between T27A3.1 and huntingtin and to determine the effect of manipulating HAP1 expression levels on the behavioral phenotype of an HD C. elegans model. These studies will serve as a basis for a larger extramural proposal to study the 19 different huntingtin interactors in C. elegans. PUBLIC HEALTH RELEVANCE: The experiments proposed in this application are aimed at characterizing the localization and function of T27A3.1, a C. elegans protein with strong similarities to mammalian Huntingtin Associated Protein 1 (HAP1) which binds to huntingtin, the protein bearing the mutation that causes Huntington's Disease, a neurodegenerative disorder affecting 1 in 10 000 individuals in the US with about 4 times more people at risk for the disease. Because of the high conservation of genes and metabolic pathways between C. elegans and humans, information obtained from these studies will help further our understanding of HD neuropathogenesis and in the design of new therapeutics. For example, if silencing or overexpression of T27A3.1 can suppress the phenotype of HD worms, then a similar strategy for manipulating the levels of HAP1 may have some benefits for patients with Huntington's Disease.